Water-Evacuator For Air Conditioner

ABSTRACT

A system and method for removing condensate from an air conditioning unit is disclosed. The system comprises a conduit including an outlet portion that is connected to a chamber of a housing of the unit at a first location. The conduit includes an inlet portion that is connected to the chamber at a second location where condensate accumulates. A gravitational separator portion which extends below the second location is connected to the outlet portion and the inlet portion. A draining portion having an orifice for allowing condensate to exit the conduit is connected to the gravitational separator portion below the second location. The first location is chosen such that during operation of the unit the pressure at the first location is less than the pressure at the second location.

CROSS-REFERENCE TO RELATED APPLICATIONS

This Application claims priority to U.S. Provisional Patent ApplicationNo.: 61/651,908 filed May 25, 2012, the disclosure of which isincorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates generally to the field of removing a liquid usingpressure differentials and gravitational forces. More specifically, theinvention relates to the field of removing condensation from confinedair conditioning modules, e.g. aircraft air conditioning modules.

2. Description of the Related Art

Air conditioning units are well known in the art, and various methodshave heretofore been utilized to drain and dispose the condensate thatis generated by air conditioners during cooling cycles. For example,condensate generated by air conditioning units in commercial buildingsmay be drained using pumps and disposed into rain gutters. Condensategenerated by air conditioning units in automobiles may be drained usinggravity and disposed on the ground underneath the automobiles via draintubes.

Air conditioning units used in aircraft may include vapor cycleevaporator drain systems to effectuate drainage of the condensate. FIG.1 shows an exemplary aircraft air conditioning unit. As can be seen fromthis figure, the air conditioning unit includes a housing having anangled face, and a drain tube extending from this angled face is used todrain the condensate generated by the unit. If the blower motor islocated close to the drain tube, effectiveness of the drain tube duringoperation of the air conditioning unit is significantly hampered.Specifically, air that is sucked into the unit's housing because of fansuction causes the pressure inside the housing to exceed the ambientpressure, which in-turn prevents the condensate from draining out thedrain tube. The condensate thus forms a pool at the floor of thehousing, and is often undesirably sprayed out the exhaust, causingdamage to the aircraft's interior and inconveniencing the passengers. Acommon prior art solution to this problem is to locate the blower at anappreciable distance from the evaporator box. However, due to thelimited space available in aircraft, this solution is not alwaysfeasible.

U.S. Pat. No. 7,543,458 to Wurth is directed to a portable vapor cyclingair conditioning unit for use with small aircraft. Wurth ('458)discloses the use of a Venturi drainage system to drain the accumulatedcondensate. Condensate is conducted from the evaporator via a drain pipeto one or more extraction Venturi tubes that are positioned in a lowpressure area in a blower. Forced air from the blower passes over theVenturi tubes and draws the moisture out of the unit. A ducting systemis provided to draw air from outside the aircraft and to dispose ofcondensate and waste heat outside the aircraft.

SUMMARY

Systems and methods for draining condensate from air conditioning unitsare disclosed herein. According to an embodiment, a system for removingcondensate from an air conditioning unit comprises a conduit includingan outlet portion that is connected to a chamber of a housing of theunit at a first location. The conduit includes an inlet portion that isconnected to the chamber at a second location where condensateaccumulation occurs. A gravitational separator portion which extendsbelow the second location is connected to the outlet portion and theinlet portion. A draining portion having an orifice for allowingcondensate to exit the conduit is connected to the gravitationalseparator portion below the second location. The first location ischosen such that during operation of the unit the pressure at the firstlocation is less than the pressure at the second location.

According to another embodiment, a method for removing condensate froman air conditioning unit that includes a housing, a blower, coils, anair intake duct, and an exhaust is disclosed. The method includes thestep of determining a first location within the housing where airpressure is lower than at a second location. The second location isbelow the first location and condensate pools at the second location. Afirst conduit with a first internal diameter is located at the firstlocation, and a second conduit with a second internal diameter islocated at the second location. The first and second conduits areconnected to a third conduit having a third internal diameter which isgenerally equal to the first internal diameter. The third conduitextends generally vertically below the second location. A fourth conduitwith a fourth internal diameter is connected to the third conduit belowthe second location. The fourth internal diameter is chosen to be lessthan the first internal diameter and the second internal diameters. Thefourth conduit has an orifice for allowing condensate to exit the fourthconduit.

According to yet another embodiment, a method for retrofitting adrainage system in an aircraft air conditioning unit comprises the stepof removing a drain pipe from a housing of the unit and plugging a holefrom which the drain pipe extended. A first location within the housingis determined where air pressure is lower than at a second locationduring operation of the unit. The second location is below the firstlocation and condensate pools at the second location. A first conduitwith a first internal diameter is located at the first location, and asecond conduit with a second internal diameter is located at the secondlocation. The first and second conduits are connected to a third conduithaving a third internal diameter which is generally equal to the firstinternal diameter. The third conduit extends generally vertically belowthe second location. A fourth conduit with a fourth internal diameter isconnected to the third conduit below the second location. The fourthinternal diameter is chosen to be less than the first internal diameterand the second internal diameters. The fourth conduit has an orifice forallowing condensate to exit the fourth conduit.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Illustrative embodiments of the present invention are described indetail below with reference to the attached drawing figures, which areincorporated by reference herein and wherein:

FIG. 1 is a perspective view of an aircraft air conditioning systemhaving a prior art drainage system.

FIG. 2 is a perspective view of the aircraft air conditioning system ofFIG. 1 having a water evacuator system in accordance with the teachingsof the current invention.

FIG. 3 is a perspective view of the aircraft air conditioning system ofFIG. 2 showing air intake and exhaust duct arrangements.

FIG. 4 is a perspective view of the aircraft air conditioning system ofFIG. 2 with a part of a housing and coils of an internal chamber removedto reveal locations of ports of the water evacuator system.

FIG. 5 is an assembly drawing showing certain equipment used to installthe water evacuator system.

FIG. 6 is a perspective view of the water evacuator system.

FIG. 7 shows the outside of the housing of the aircraft air conditioningsystem of FIG. 2 illustrating the location of installation of the waterevacuator system.

FIG. 8 shows inner diameters of conduits and a drain of the waterevacuator system, and includes arrows depicting the flow of air andcondensation.

FIG. 9 shows a height of a drop between an induction tube and the drainof the water evacuator system,

FIG. 10 shows the inner diameters of the water evacuator system'sconduits and drain, as well as the corresponding pressures.

FIG. 11 shows the inner diameters of the water evacuator system'sconduits and drain, as well as the corresponding mass flow rates.

FIG. 12 shows the pressure loss per unit length,

FIGS. 13A-C show possible design variations of the water evacuatorsystem in accordance with the teachings of the current invention.

DETAILED DESCRIPTION

Embodiments of the present invention provide systems and a method forremoving condensate from an air conditioning unit in which size and/orweight are restricted.

A prior art version of an aircraft air conditioning drainage system isshown in FIG. 1. Referring to the figure, an air conditioning unit 10has both a cooling portion 12 and an air-handling portion 14. Thecooling portion 12 receives unconditioned air from an intake 16 into achamber inside a housing 18 which includes cooling coils (coils 134shown in FIG. 3). The air-handling portion 14 includes a motor withhousing 20 used to operate a blower 22 in a known manner. Air receivedinto intake 16 is drawn through the heat-exchanging coils in the housing18 and then out an exhaust 24. The coils receive a circulation of aheat-transfer medium (e.g., refrigerant R-12, R134) from conduits, e.g.,hoses or pipes, through connections made into couplers 26 and 28 in aknown fashion.

In operation, the heat-exchanging coils in the chamber in the housing 18develop condensate which drips to form a pool at the floor of thehousing 18. This pooling of condensate has been conventionally handledusing a drain tube 30 which extends out from an angled side face 32 ofthe prior art air conditioning unit 10 shown in FIG. 1. Theeffectiveness of the drain tube 30 is limited. With the blower motor on,the drain 30 does not eliminate pooling within the chamber in thehousing 18, and therefore, a significant amount of condensate remains atthe floor of the housing 18 and on the heat-exchanger coils.Specifically, the ambient barometric pressure at the far end of draintube 30 is greater than pressure inside the housing chamber due to fansuction, so air is sucked into housing 18 and water does not drainproperly. Because of this, sudden blasts of water are emitted out of theexhaust 24 when the amount of water collected is high. The sprayed watercan cause water damage to the aircraft interior, and also disturbpassengers. Water will only drain properly from the air conditioningunit 10 when the motor is off and the pressure is equalized.

FIGS. 2-13 illustrate an improvement over the arrangement shown inFIG. 1. Referring first to FIG. 2, it can be seen that much of thesystem is just like the prior art version shown in FIG. 1. As shown, airconditioning unit 110 of FIG. 2 has both cooling 112 and air-handling114 portions, an air intake 116, a housing 118 for cooling coils 134(see FIG. 3), a motor with housing 120, a blower 122, an exhaust 124,couplers 126 and 128, and an angled side face 132, all like in theconventional air conditioning unit 10 shown in FIG. 1.

Looking at the angled side face 132 in FIG. 2 reveals, however, that thedrain tube 30 seen in FIG. 1 has been removed, and the hole where thestem existed has been eliminated. Where a retrofit is made to anexisting air conditioning unit in the field, the tube 30 may be removed,and the hole from which drain tube 30 emanates may be plugged orotherwise sealed. Where the air conditioning unit 110 is anewfabrication, it can be designed with a housing 118 that does not includea drain stem (stem 30 is removed as shown in FIG. 2).

Referring to FIG. 3, it can be seen that a condensation removal device130 (a system of conduits) has been added to the overall airconditioning unit 110 on the side of the housing 118 where the blower122 is attached. Known through analysis of experimentation, device 130accesses a low pressure location in the housing 118 and uses theresulting suction to draw condensate out of the unit 110. The condensateis then taken out of the flowing air using a gravitational drain. Thefront of the housing 118 and the internal heat exchanger coils have beencut away in FIG. 4 to reveal where an induction port 140 drawscondensate from the floor 143 of the housing 118 where most of thecondensate accumulation occurs. Another port 148 is connected into thechamber at a location where pressure is lower than at the induction port140. The force from the weight of the water further reduces the pressureat the inlet 140, thus providing more potential energy, or pressuredifferential, so the water will actively seek the lower pressure inlet148. It has been determined that the location of port 148 as shown inFIG. 4 is optimal because it is (i) immediately outside of the mouth 121of the blower; (ii) above a horizontal plane which passes through acenter axis of the blower; and, (iii) on the side opposite the blowerexhaust 124, and as such, is exposed to especially low pressure. Thiscreates the suction necessary to remove the condensate through port 140.

The specifics regarding the conduit system 130 which performs thecondensation removal can be seen in FIGS. 5 and 6. Beginning with theinduction port 140, a straight portion 141 may extend to an elbow 142,then into another straight portion 144 where it may be connected into anelbow 156 which is a part of the drainage portion of the device 130.

The low pressure/suction port 148 may be incorporated into the conduitsystem 130 via straight section 149, which may extend to an elbow 150. Astraight section 152 may extend from the elbow 150 to an elbow 154. Avertical gravitational separation section 146 may extend from the elbow154 to an elbow 155, which may connect to a reverse elbow 156. Astraight drainage section 158 may extend beneath the reverse elbow 156.The straight drainage section 158 may be capped from below by a flatbottom 157. A metered drainage stem 160 may extend from section 158 andmay have an orifice 164. Stem 160 may extends horizontally and backwardsrelative to the unit 110. A rib 162 may be used to receive a hose ortubing (not shown) and secure it over and onto the drainage stem 160.This hose (or tubing) may drain the condensate to: (i) outside theaircraft, (ii) a temporary storage vessel, or (iii) some other vessel orconduit network so that the condensate may be recycled and used for somepurpose inside the aircraft.

FIG. 5 also shows the devices used to secure the condensate removaldevice 130 onto the housing 118. First, a bracket 165, which maycomprise a large flange 167 and a short flange 166, may be fastened ontoa shelf 117 made into the housing 118 as can he seen in FIG. 7. A pairof screws 176 and 178 may he installed into nuts (only one nut 186 isvisible in FIG. 7) from inside the housing 118.

A large collar 168 and a small collar 170 may be used to secure ends ofthe low pressure/suction port 148 and the induction port 140,respectively, to the large flange 167 as shown in FIG. 5 using fasteners172, 174 and receiving nuts 180, 182. The end of the low pressure port148 may pass through a rectangular aperture 169 formed in the bracket165. FIG. 7 shows where and how the ends of the low pressure andinduction ports (148 and 140, respectively) are connected to the outerwall of the housing 118.

FIG. 8 shows the internals of conduit network 130, and the movement ofboth air (A) and condensate (C) using arrows so labeled. As can be seenin the figure, low pressures at port 148 may cause air (A) to be drawninto induction port 140, up vertical gravitational separation section146, and then out the port 148. When this occurs, condensate (C) ispulled into port 140 along with the air (A). Once the vertical section146 is reached, however, the condensate (C) may separate from the air(A) as shown. This is due to gravity, in that the relatively lowerpressures existing at port 148 result in the air (A) to be drawn up andout port 148, while the condensate (C), which is too heavy, separatesfrom the airflow. Once separated, the condensate (C) drops down intosection 158 and exits from the drain stern 160 (i.e., orifice 164),where it may be recycled or discarded (e.g., by using drain hose ortubing (not shown)).

Referring now to FIG. 9, a value for height h_(c) is determined whichwill result in the water condensate C to drain out tube 144 into tube146 and be emitted out of the metered drainage system 160. The pressuresP₁, P₂, and P₀ (FIG. 10) at the orifices of device 130 drive the waterevacuation process. Pressure seen at orifice 148 (P₁) is less than thepressure seen at orifice 140 (P₂) which is less than the ambientpressure (P₀) seen at orifice 164 of the metered drainage system 160.That is:

P₁<P₂<P₀

Variable h_(c), the height necessary in tube 158 for proper draining, ismeasured from the lower part of the connection of tube 144 and 158 tothe upper part of the connection of tube 164 and 158 (see FIGS. 9 and10). h_(c) can be determined according to the following relationship:

P ₁ =λ·h _(c)

Resulting in:

$\mspace{20mu} {\text{?} = {{abs}{\frac{P_{1}}{\lambda}}}}$?indicates text missing or illegible when filed

where:

λ = Specific  weight  of  the  pool  fluid${abs}{{= {{{Absolute}\mspace{14mu} {value}\mspace{14mu} {of}\mspace{14mu} \frac{P_{1}}{\lambda}P_{1}} = {{Gauge}\mspace{14mu} {Pressure}\mspace{14mu} {at}\mspace{14mu} {port}\mspace{14mu} 148.}}}}$

Variable h_(c), as determined, is the minimum height necessary. It ispermissible (and recommended) to make the height, h_(c) some percentagegreater than the minimum (e.g., 10%-25% higher). This design factor ofsafety will account for any pressure or voltage transients.

The inner diameters (D₁, D₂, D₃) of each of conduit sections 152, 144,and 160 play a significant role in draining the fluid properly. Innerdiameter D₁, in the preferred embodiment, exists not only at orifice148, but also through portion 149 (see FIG. 6), around bend 150, throughthe length of portion 152, down through bend 154 and the length ofvertical gravitational separator portion 146 all the way to floor 157. Asecond inside diameter D₂ exists not only at orifice 140, but also thelength of portion 144 until it feeds into the vertical separator portion146. A third diameter D₃ exists not only at orifice 164 but also alongthe entire length of drain stem 160.

These diameters (D₁, D₃) have been proportioned in a manner that createsa desired result in the vertical separator portion 146. This effect issymbolized, and can be best understood by following the paths of thearrows representing airflow (A) and condensate flow (C) in FIG. 8. Asthe suction is administered at orifice 140 as the result of herelatively low pressure existing at orifice 148, both air (A) and anycondensate in the proximity of orifice 140 are drawn into and alongportion 144. Upon reaching the vertical separator portion 146, the air(A) will continue to rise, travel around bend 154 and exit the system atorifice 148 into the low pressure area in the chamber near the mouth 121of the blower (see FIG. 4). The condensate (C), however, because it hasa higher specific weight than the air (A), becomes separated uponreaching the vertical separator portion 146, drops to floor 157,collects and then passes through stem 160, and out orifice 164 into thedrain tubing/hose (not shown).

Quantification of the relationship between inner diameters D₁, D₂ and D₃is critical in optimizing drainage capability. Referring to FIG. 11,{dot over (m)}₁, {dot over (m)}₂, {dot over (m)}₃ are the mass flowrates at orifices 148, 140, and 164, and each instance, is determinedaccording to the formula:

{dot over (m)}=ρ·V·A

where: ρ=Fluid Density

-   -   V=Fluid Velocity    -   A=Tube Cross-Sectional Area

In order to optimize water drainage into port 140, and subsequently outof orifice 164, it is necessary to optimize D₁, D₂ and D₃ such that {dotover (m)}₂ is greatest.

The first mode of operation analyzed is when there is no water in thesystem.

{dot over (m)} ₁ −{dot over (m)} ₂ −{dot over (m)} ₃=0

ρ₁ ·V ₁ ·A ₁−ρ₂ ·V ₂ ·A ₂ −ρ ₃ ·V ₃ ·A ₃=0

where: ρ₁=ρ₂=ρ₃

Knowing:

$A_{1} = {\pi \cdot \left( \frac{D_{1}}{2} \right)^{2}}$$A_{2} = {\pi \cdot \left( \frac{D_{2}}{2} \right)^{2}}$$A_{3} = {\pi \cdot \left( \frac{D_{3}}{2} \right)^{2}}$

where:

-   -   D₁=Tube Diameter at orifice 148    -   D₂=Tube Diameter at orifice 140    -   D₃=Tube Diameter at orifice 164

Simplified:

V ₁ ·A ₁ −V ₂ ·A ₂ −V ₃ ·A ₃=0

Q ₁ −Q ₂ −Q ₃=0

Where:

-   -   Q₁=Volumetric Flow Rate at orifice 148    -   Q₂=Volumetric Flow Rate at orifice 140    -   Q₃=Volumetric Flow Rate at orifice 164

Ideally Q₃, or the volumetric flow rate through orifice 164, should beno more than 5% that of Q₁. This means that there should be no more thana 5% pressure loss from Q₁ as a result of D₃, which in-turn means thatD₃ will be smaller than D₁ or D₂.

However, D₃ should not be so small that it restricts the collectedcondensate from draining properly. The minimum drain diameter D₃ forallowing collected condensate to properly drain may be computed asfollows:

Q ₃ =V _(Jet) ·A ₃

where: V_(Jet)=Fluid Exit Velocity Due to Gravity

-   -   A₃=Tube Cross-Sectional Area at D₃        and:

V _(Jet)=√{square root over (2·g·h _(c))}

where: g=Acceleration Due to Gravity

-   -   h_(c)=Height in tube 158

In small systems, typical values of Q₃ will be between 0.5 and 1in³/sec. The goal is to find a specific value or optimum range for D₃.By using the equations above to solve for D₃:

$D_{3} = \frac{\sqrt{2 \cdot Q_{3} \cdot \pi \cdot g \cdot h_{c}} \cdot \sqrt[4]{2 \cdot g \cdot h_{c}}}{\pi \cdot g \cdot h_{c}}$

This is the minimum value of D₃ such that the pooled condensate willadequately flow out of the system. People of skill in the art willappreciate that the equation above may be used to approximate orcalculate the minimum value of D₃, and that a conduit section of thenext standard size above this approximated or calculated value may beutilized in the device 130.

As stated above should be no more than 5% of Q₁. This sets the maximumvalue for Q₃.

So:

$Q_{3} = {\frac{1}{20} \cdot Q_{1}}$$\frac{\pi \cdot D_{3}^{2} \cdot V_{3}}{4} = {\left( \frac{1}{20} \right) \cdot \frac{\pi \cdot D_{1}^{2} \cdot V_{1}}{4}}$

Reduces to:

${D_{3}^{2} \cdot V_{3}} = {\left( \frac{1}{20} \right) \cdot D_{1}^{2} \cdot V_{1}}$

For simplicity, if V₃=V₁ then,

D ₃=0.224·D ₁

Or:

$\frac{\sqrt{2 \cdot Q_{3} \cdot \pi \cdot g \cdot h_{c}} \cdot \sqrt[4]{2 \cdot g \cdot h_{c}}}{\pi \cdot g \cdot h_{c}} < D_{3} < {{.224} \cdot D_{1}}$

Another way to ensure that pressure P3 is less than pressures P1 and P2is to create a pressure drop.

The pressure drop caused by tube shear stress (see FIG. 12) is:

${\Delta \; P} = {4 \cdot \tau_{w} \cdot \left( \frac{L}{D} \right)}$

where:

-   -   ΔP=Pressure loss in tube    -   L=Tube length    -   D=Tube diameter    -   τ_(w)=Tube wall shear stress        Referencing the formula above, in order to make ΔP→∞, either        τ_(w) needs to be very large or

$\left( \frac{L}{D} \right)$

needs to be very large. L, or the length of tube 160, can be made to belong enough to cause a great enough pressure drop within tube 160.

Continuing from above for the equal density mode:

Q₁ − Q₂ − Q₃ = 0 ${Q_{1} - Q_{2} - {\frac{1}{20}Q_{1}}} = 0$${{\frac{19}{20}Q_{1}} - Q_{2}} = 0$ $Q_{2} = {\frac{19}{20}Q_{1}}$

Where:

Q ₁ =V ₁ ·A ₁

Q ₂ =V ₂ ·A ₂

Expanded:

${V_{2} \cdot A_{2}} = {\frac{19}{20}{V_{1} \cdot A_{1}}}$

Where:

$V_{1} = \left( \frac{{- 2} \cdot P_{1}}{\rho_{1\;}} \right)^{\frac{1}{2}}$$V_{2} = \left( \frac{2 \cdot \left( {P_{2} - P_{1}} \right)}{\rho_{2}} \right)^{\frac{1}{2}}$

-   -   P₁=Gauge Pressure at Orifice 148    -   P₂=Gauge Pressure at Orifice 140    -   ρ₁=Fluid density at Orifice 148    -   ρ₂=Fluid density at Orifice 140

Resulting:

$\left\lbrack \frac{D_{2}}{D_{1}} \right\rbrack = {\left\lbrack \frac{- P_{1}}{\left\lbrack {P_{2} - P_{1}} \right\rbrack} \right\rbrack^{\frac{1}{4}} \cdot \left\lbrack \frac{19}{20} \right\rbrack^{\frac{1}{2}}}$

The above equation is determined for the system without pooledcondensate, thus there is nothing to drain. Generally the higher thepressure difference between P₁ and P₂ the smaller the change there needsto be between D₁ and D₂. Under normal conditions P₁<P₂ and D₂ will needto be greater than D₁. Generally,

D₂≈1.15·D ₁

Again, this is for a system that has similar fluid densities in alltubes.

Now for the analysis of the system with fluid condensate in tube D₂

{dot over (m)} ₁ −{dot over (m)} ₂ −{dot over (m)} ₃=0

ρ₁ ·V ₁ ·A ₁−ρ₂ ·V ₂ ·A ₂−ρ₂ ·V ₃ ·A ₃=0

ρ₁≠ρ₂

Where: ρ₃=ρ₁

V₁=V₃

D ₃=0.224·D ₁

Resulting:

ρ₁ ·V ₁ ·A ₁−ρ₂ ·V ₂ ·A ₂−ρ₁ ·V ₃ ·A ₃=0

Simplifying:

0.95ρ ₁ ·V ₁ ·D ₁ ²=ρ₂ ·V ₂ ·D ₂ ²

Resulting

$\left\lbrack \frac{D_{2}}{D_{1\;}} \right\rbrack = {\left\lbrack \frac{{- \rho_{1}} \cdot P_{1}}{\rho_{2} \cdot \left\lbrack {P_{2} - P_{1}} \right\rbrack} \right\rbrack^{\frac{1}{4}} \cdot \left\lbrack \frac{19}{20} \right\rbrack^{\frac{1}{2}}}$

The goal is to get some value for D₁ and D₂ that will work efficientlywhen there are similar and dissimilar fluid densities. Taking the rootmean square obtains an average value of the two varying quantities.

$\left\lbrack \frac{D_{2}}{D_{1}} \right\rbrack_{Total}^{2} = {{\frac{1}{2} \cdot {\left\lbrack {\left\lbrack \frac{D_{2}}{D_{1\;}} \right\rbrack_{\rho_{1} = \rho_{2}}^{2} + \left\lbrack \frac{D_{2}}{D_{1}} \right\rbrack_{\rho_{1} \neq \rho_{2}}^{2}} \right\rbrack \left\lbrack \frac{D_{2}}{D_{1}} \right\rbrack}_{Total}^{2}} = {\left\lbrack \frac{19}{40} \right\rbrack \cdot \left\lbrack {\frac{- P_{1}}{\left\lbrack {P_{2} - P_{1}} \right\rbrack} + \left\lbrack \frac{{- \rho_{1}} \cdot P_{1}}{\rho_{2} \cdot \left\lbrack {P_{2} - P_{1}} \right\rbrack} \right\rbrack} \right\rbrack^{\frac{1}{2}}}}$

The equation above will be better used as an inequality. In this case:

$D_{3} < \left\lbrack \frac{D_{2}}{D_{1}} \right\rbrack_{Total}^{2} \leq {\left\lbrack \frac{19}{40} \right\rbrack \cdot \left\lbrack {\frac{- P_{1}}{\left\lbrack {P_{2} - P_{1}} \right\rbrack} + \left\lbrack \frac{{- \rho_{1}} \cdot P_{1}}{\rho_{2} \cdot \left\lbrack {P_{2} - P_{1}} \right\rbrack} \right\rbrack} \right\rbrack^{\frac{1}{2}}}$

Or simply stated:

$D_{3} < D_{2} \leq {D_{1} \cdot \left\lbrack {\left\lbrack \frac{19}{40} \right\rbrack \cdot \left\lbrack {\frac{- P_{1}}{\left\lbrack {P_{2} - P_{1}} \right\rbrack} + \left\lbrack \frac{{- \rho_{1}} \cdot P_{1}}{\rho_{2} \cdot \left\lbrack {P_{2} - P_{1}} \right\rbrack} \right\rbrack} \right\rbrack^{\frac{1}{2}}} \right\rbrack^{\frac{1}{2}}}$

Thus, as can be appreciated from the equation above, D₂ needs to begreater than D₃ but less than some quantity times D₁.

Generally speaking, D₁ will be about 1.5 to 2.5 times the value of D₂.Using a ratio that is considerably smaller, for instance,

D₁≈0.5·D₂

will choke down the flow rate of the denser fluid, thus causing the flowrate to be limited through orifice 140. The effect will be a slowerdrain time out of orifice 140. Conversely, if the ratio is larger,

D₁≈3·D₂

the flow rate out of orifice 140 will be above maximum but excesspressure from P₁ might be lost through orifice 140. The final diametersof D₁ and D₂ should be determined through experimentation in line withmanufacturing limitations.

One thing to note is that for the water to properly flow, the pressureseen at orifice 148 needs to be less than the pressure seen at orifice140. If P₁>P₂ but less than P₀ (ambient pressure) the water seen at port140 will not flow out, thus causing spray. So the ratio should be:

$\left( \frac{P_{1} - P_{0}}{P_{2} - P_{0}} \right) > 1$

Also, for more efficient drainage, (P₁−P₀) needs to be greater than(P₂−P₀). Drain potential increases with the greater (P₁−P₀) is ascompared to (P₂−P₀).

In summary, the design process begins with determining the negativepressure within air conditioning console. Specifically, the locationwithin the console where air pressure is the lowest is determined, andthe fluid induction conduit inlet (e.g., orifice 1301 a in FIG. 13A;orifice 1301 b in FIG. 13B) is located as near as possible to this lowpressure area. Next the location in the console where condensate fluidhas the propensity to collect is determined, and the fluid inductiontube is located there; for example, orifice 1302 a in FIG. 13A andorifice 1302 b in FIG. 13B are each located at locations where condensedwater will collect. Pressure values at location P₁ and P₂ are thendetermined.

Next, the height drop between induction tube 1301 c (see FIG. 13 c) anddrain 1302 c is determined. This is done using the relation:

$h_{c} = {{abs}{\frac{P_{1}}{\lambda}}}$

The drop height typically ranges from 0.5 inches to 3 inches dependingon how much negative pressure is within the unit. Experimentation willdetermine the negative pressure within the unit.

Next, a value for D₃ is determined. D₃ needs to be large enough to allowthe fluid to drain out depending on the rate of pooling, but smallenough to not allow pressure loss from P₁ or P₂.

$\frac{\sqrt{2 \cdot Q_{3} \cdot \pi \cdot g \cdot h_{c}} \cdot \sqrt[4]{2 \cdot g \cdot h}}{\pi \cdot g \cdot h_{c}} < D_{3} < {{.224} \cdot D_{1}}$

Based off the information above, an adequate value for diameter D₁ iscomputed.

D₁≈4.5·D₃

The final criterion is to determine drain diameter D₂, which can begleaned by substantially satisfying the relation:

$D_{3} < D_{2} \leq {D_{1} \cdot \left\lbrack {\left\lbrack \frac{19}{40} \right\rbrack \cdot \left\lbrack {\frac{- P_{1}}{\left\lbrack {P_{2} - P_{1}} \right\rbrack} + \left\lbrack \frac{{- \rho} \cdot P_{1}}{\rho_{2} \cdot \left\lbrack {P_{2} - P_{1}} \right\rbrack} \right\rbrack} \right\rbrack^{\frac{1}{2}}} \right\rbrack^{\frac{1}{2}}}$

The following example illustrates these computations.

Example:

$\rho_{1} = {{{air}\left( {{.0024}\; \frac{slugs}{{ft}^{3}}} \right)} = \left( {0.0000013889\frac{slugs}{{in}^{3}}} \right)}$$\rho_{2} = {{{water}\left( {1.94\; \frac{slugs}{{ft}^{3}}} \right)} = \left( {0.0011227\; \frac{slugs}{{in}^{3}}} \right)}$$\lambda_{water} = {{62.30\; \frac{lb}{{ft}^{3}}} = {{.0361}\; \frac{lb}{{in}^{3}}}}$P₁ = −.060  psi(gauge) P₂ = −.030  psi(gauge)$Q_{3} = {{.75}\; \frac{{in}^{3}}{\sec}}$$h_{c} = {{{abs}{\frac{P_{1}}{\lambda}}} = {{{abs}{\frac{{- {.060}}\; \frac{lb}{{in}^{2}}}{{.0361}\; \frac{lb}{{in}^{3}}}}} = {1.66\mspace{14mu} {inches}}}}$

Add 10% to account for transients

1.66·1.1=1.83 inches

Now determine diameter D₃.

$\frac{\sqrt{2 \cdot Q_{3} \cdot \pi \cdot g \cdot h_{c}} \cdot \sqrt[4]{2 \cdot g \cdot h}}{\pi \cdot g \cdot h_{c}} < D_{3}$${\frac{\sqrt{2 \cdot {.75} \cdot \pi \cdot 386.1 \cdot 1.66} \cdot \sqrt[4]{2 \cdot 386.1 \cdot 1.66}}{\pi \cdot 386.1 \cdot 1.66} < D_{3}}->{{\frac{\sqrt{3020.3} \cdot \sqrt[4]{1281.9}}{2013.5} < D_{3}}->{{.1633} < D_{3}}}$

So D₃ needs to be larger than 0.1633 inches.

For Manufacturing D₃=0.17

Determine diameter D₁.

D₁≈4.5·D₃

D₁≈4.5·0.17

D₁≈0.765 inches

Rounding up:

D₁ will be 0.80 inches in diameter

Determine diameter D₂.

$\mspace{20mu} {D_{2} \leq {D_{1} \cdot \left\lbrack {\left\lbrack \frac{19}{40} \right\rbrack \cdot \left\lbrack {\frac{- P_{1}}{\left\lbrack {P_{2} - P_{1}} \right\rbrack} + \left\lbrack \frac{{- \rho_{1}} \cdot P_{1}}{\rho_{2} \cdot \left\lbrack {P_{2} - P_{1}} \right\rbrack} \right\rbrack} \right\rbrack^{\frac{1}{2}}} \right\rbrack^{\frac{1}{2}}}}$$D_{2} \leq {{.8} \cdot \left\lbrack {\left\lbrack \frac{19}{40} \right\rbrack \cdot \left\lbrack {\frac{- \left( {- 0.6} \right)}{\left\lbrack {\left( {- {.03}} \right) - \left( {- {.06}} \right)} \right\rbrack} + \left\lbrack \frac{{- (0.0000013889)} \cdot \left( {- {.06}} \right)}{\begin{matrix}{(0.0011227) \cdot} \\\left\lbrack {\left( {- {.03}} \right) - \left( {- {.06}} \right)} \right\rbrack\end{matrix}} \right\rbrack} \right\rbrack^{\frac{1}{2}\;}} \right\rbrack^{\frac{1}{2}}}$$\mspace{20mu} {D_{2} \leq {{.8} \cdot \left\lbrack {\left\lbrack \frac{19}{40} \right\rbrack \cdot \left\lbrack {2 + {.002474}} \right\rbrack^{\frac{1}{2}}} \right\rbrack^{\frac{1}{2}}}}$$\mspace{20mu} {D_{2} \leq {{.8} \cdot \lbrack{.6722}\rbrack^{\frac{1}{2}}}}$  D₃ ≤ D₂ ≤ .656  inches   D₂ ≈ .63  inches  where  D₃ = .17  inches

It should be understood that instead of providing conduits havinginternal diameters which are constant lengthwise, the internal diameterscould be varied and the desired fluid mechanics obtained by restrictingflow through the minimum internal diameters at locations (e.g., at theorifices). Thus, it is possible that this sort of variation could bemade and the desired drainage arrangement maintained.

Many different arrangements of the various components depicted, as wellas components not shown, are possible without departing from. the spiritand scope of the present invention. Embodiments of the present inventionhave been described with the intent to be illustrative rather thanrestrictive. Alternative embodiments will become apparent to thoseskilled in the art that do not depart from its scope. A skilled artisanmay develop alternative means of implementing the aforementionedimprovements without departing from the scope of the present invention.

It will be understood that certain features and subcombinations are ofutility and may be employed without reference to other features andsubcombinations and are contemplated within the scope of the claims. Notall steps listed in the various figures need be carried out in thespecific order described.

The invention claimed is:
 1. A system for removing condensate from anair conditioning unit, the air conditioning unit having a housingincluding a chamber, a blower, coils, an air intake duct, and anexhaust, the system comprising: a conduit comprising: an outlet portionhaving a first port, the first port being coupled to the chamber at afirst location; an inlet portion having a second port, the second portbeing coupled to the chamber at a second location where condensateaccumulation occurs, the second location being below the first location;a gravitational separator portion connected to the outlet portion andthe inlet portion, the gravitational separator portion extending belowthe second location; and a draining portion having an orifice forallowing condensate to exit the conduit, the draining portion connectedto the gravitational separator portion below the second location;wherein during operation of the air conditioning unit, the pressure atthe first location is less than the pressure at the second location. 2.The system of claim 1 wherein: the conduit generally resides outside thehousing; and the air conditioning unit is configured for use inaircraft.
 3. The system of claim 2 wherein: the conduit is of a unitaryconstruction; and during operation of the air conditioning unit thepressure at the second location is less than the pressure at theorifice.
 4. The system of claim 3, wherein: the outlet portion and thegravitational separator portion have a first internal diameter; theinlet portion has a second internal diameter; the draining portion has athird internal diameter; and the third internal diameter is less thanthe second internal diameter.
 5. The system of claim 4 wherein thesecond internal diameter is less than the first internal diameter. 6.The system of claim 4 wherein the first internal diameter is greaterthan the second internal diameter and less than 2.5 times the secondinternal diameter.
 7. The system of claim 4 wherein the first internaldiameter is about 4.5 times the third internal diameter.
 8. The systemof claim 4 wherein the first internal diameter is about 0.80 inches, thesecond internal diameter is about 0.63 inches, and the third internaldiameter is about 0.17 inches.
 9. The system of claim 4 wherein: theinlet portion has a top surface and a bottom surface; the drainingportion has a top surface and a bottom surface; and the verticaldistance between the inlet portion bottom surface and the drainingportion top surface is between about 0.5 inches and about 3 inches. 10.A method for removing condensate from an air conditioning unit, the airconditioning unit having a housing, a blower, coils, an air intake duct,and an exhaust, the method comprising: determining a first locationwithin the housing where during operation of the air conditioning unitair pressure is lower than at a second location; determining the secondlocation within the housing where pooling of condensate occurs, thesecond location being below the first location; locating a first conduitwith a first internal diameter at the first location; locating a secondconduit with a second internal diameter at the second location;connecting the first conduit and the second conduit to a third conduitwith a third internal diameter that is generally equal to the firstinternal diameter, the third conduit extending generally verticallybelow the second location; and connecting a fourth conduit with a fourthinternal diameter to the third conduit below the second location;wherein the fourth internal diameter is less than the first internaldiameter and the second internal diameter; wherein the fourth conduithas an orifice for allowing condensate to exit the fourth conduit. 11.The method of claim 10 wherein the first location is: adjacent a mouthof the blower; and above a horizontal plane that passes through acentral axis of the blower.
 12. The method of claim 10 wherein: thesecond conduit has a top surface and a bottom surface; the fourthconduit has a top surface and a bottom surface; and a height drop in thethird conduit between the second conduit bottom surface and the fourthconduit top surface is determined by dividing an absolute value of thepressure at the first location by the fluid density of water.
 13. Themethod of claim 13 wherein; the first internal diameter is about 0.80inches; the second internal diameter is about 0.63 inches; and thefourth internal diameter is about 0.17 inches.
 14. The method of claim12 wherein the fourth internal diameter is proportional to the heightdrop and a volumetric flow rate of condensate in the fourth conduit. 15.The method of claim 12 wherein a minimum value for the fourth internaldiameter is one of approximated or calculated using the relationship:$D_{4} = \frac{\sqrt{2 \cdot Q_{4} \cdot \pi \cdot g \cdot h_{c}} \cdot \sqrt[4]{2 \cdot g \cdot h_{c}}}{\pi \cdot g \cdot h_{c}}$wherein: D₄ is the fourth internal diameter; Q₄ is the volumetric flowrate of condensate in the fourth conduit; g is the acceleration due togravity; and h_(c) is the height drop.
 16. The method of claim 12wherein the first internal diameter, the second internal diameter, andthe fourth internal diameters are chosen to substantially satisfy thefollowing relationship:$D_{4} < D_{2} \leq {D_{1} \cdot \left\lbrack {\left\lbrack \frac{19}{40} \right\rbrack \cdot \left\lbrack {\frac{- P_{1}}{\left\lbrack {P_{2} - P_{1}} \right\rbrack} + \left\lbrack \frac{{- \rho_{1}} \cdot P_{1}}{\rho_{2} \cdot \left\lbrack {P_{2} - P_{1}} \right\rbrack} \right\rbrack} \right\rbrack^{\frac{1}{2}}} \right\rbrack^{\frac{1}{2}}}$wherein: D₄ is the fourth internal diameter; D₂ is the second internaldiameter; D₁ is the first internal diameter; P₁ is the pressure at thefirst location; P₂ is the pressure at the second location; ρ₁ is thefluid density of air; and ρ₂ is the fluid density of water.
 17. Themethod of claim 12 further comprising the step of connecting the fourthconduit to a tube for routing outside the unit for recycling condensateexiting the orifice.
 18. A method for retrofitting a drainage system inan aircraft air conditioning unit having a housing, a blower, coils, anair intake duct, and an exhaust, the method comprising removing a drainpipe from the housing; plugging a hole from which the drain pipeextended; determining a first location within the housing where airpressure is lower than at a second location during operation of theunit; determining the second location within the housing where poolingof condensate occurs, the second location being below the firstlocation; locating a first conduit with a first internal diameter at thefirst location; locating a second conduit with a second internaldiameter at the second location; connecting the first conduit and thesecond conduit to a third conduit with a third internal diameter that isgenerally equal to the first internal diameter, the third conduitextending generally vertically below the second location; and connectinga fourth conduit with a fourth internal diameter to the third conduitbelow the second location; wherein the fourth internal diameter is lessthan the first internal diameter and the second internal diameter;wherein the fourth conduit has an orifice for allowing condensate toexit the fourth conduit.
 19. The method of claim 18 wherein: the firstinternal diameter is greater than the second internal diameter; and thefirst location is adjacent a mouth of the blower and above a horizontalplane that passes through a central axis of the blower.
 20. The methodof claim 19 further comprising the step of connecting the fourth conduitto a tube for routing outside the unit for recycling condensate exitingthe orifice.